Triaryl phosphates and other phosphate esters have been used as fire-resistant hydraulic fluids and lubricants for some years. A problem with these fluids is that they tend to degrade, especially by hydrolysis if water is present in the fluid, to generate acidic products, potentially including phosphoric acid, that may impair the properties of the fluids and/or corrode the equipment in which they are used. It has therefore been proposed to remove the acid products, and one way of removing them is by means of an ion exchange resin. This has proved to be an extremely successful solution. However, over time, the resin needs to be changed. To facilitate this, it is common to provide the ion exchange resin in a radial-flow cartridge.
In use, the ion exchange resin tends to swell as its water content increases, and to contract as its water content decreases. Thus, it is desirable to fill, store, and supply the cartridges with a relatively low moisture content in the ion exchange resin, both to avoid the possibility of water exuding from the cartridges in storage or handling, and to provide cartridges which are designed to absorb as much water as possible. However, it has been determined that when the ion exchange cartridges are used on fluids having a high initial total acid number (TAN), the expansion of the resin can generate forces sufficient to swell, or even burst, the cartridge.
To prevent bursting, partially filled cartridges have been proposed. The goal was to allow the vacant space in the cartridge to accommodate the expansion of the resin. However, since ion exchange resin is loose, it tends to settle at the bottom of the cartridge, leaving the expansion space at the top end. As such, the resin tends to pack within the cartridge. The tight packing of the resin inhibits upward movement as the resin expands. As such, the sides of the cartridge are, again, subject to excessive forces. In addition, it has been determined that a partially filled cartridge can lead to the development of pockets of open spaces through which the circulating fluid may bypass the resin, reducing the efficiency of the ion exchange.
A need, therefore, exists for an improved ion exchange resin cartridge which is designed to provide efficient moisture removal while reducing the occurrence of bursting.